Yeah occasionally mixing a singular "they" that way is very common in english in certain contexts. Particularly when its short clear paragraphs talking about a single person. But that's still a distinction from being used as a pronoun everywhere, which can definitely get confusing quickly, even for non-ESL readers... which is all that really matters in writing/communication.

I'm seeing it more often in journalism now where multiple people or organizations are referred to through out an article and then "they" gets thrown in liberally for social etiquette. It takes serious mental effort to keep track of who they are referring to. Might as well just always use their name at that point to avoid both conflict and confusion shrug.